corn Seeding Rates And Maturity Selection · NE-IPM Module #12 Corn Seeding Rates and Maturity Selection p. 1 Corn Seeding Rates and Maturity Selection

NE-IPM Module #12 Corn Seeding Rates and Maturity Selection p. 1

www.nysaes.cornell.edu/ipmnet/ne.ipm.region

Corn Seeding Rates andMaturity Selection

Compiled by Janice Degni and Mary M. Woodsen

Overview

This module takes place in two sessions over a span of weeks.

♦ Activity #1 is best adapted to farms from northern Pennsylvania through New England. Conduct it prior toplanting, preferably prior to seed purchase.

♦ Activity #2 also takes place it prior to planting, preferably prior to seed purchase. It applies to all areas of theNortheast.

♦ Activity #3 goes with Activity #1 but takes place in the field after germination.

Concept Activity Handouts

To select optimal seeding rates for corn, you need tounderstand the role of “yield potential” indetermining harvest populations, the benefits ofdensely planted stands, and how planting datesand conditions affect drop rates.

#1: PreplantingDecisions on SeedingRates

A. Optimum Corn SeedingRates: Grain and Silage

To select the right hybrids for their farm and hedgetheir bets for the highest overall yields seasonafter season, participants should understandhow “growing degree days” determine seasonlength and learn how to apply the 20/60/20 rule.

#2: About GDDs andthe 20/60/20 Rule.

B. Understanding GrowingDegree Days (GDDs

C. Northeast GDD Map)

D. Planning Sheet for CornPlanting (optional)

To plan for coming years, participants shouldevaluate their seeding rate plan by checking itagainst actual field conditions.

Ask participants to bring past records if they have them.

#3: Verifying PlantPopulations

E. Plant Population Card

ResourcesCornell Field Crops and Soils HandbookCorn Management/Diagnostic Guide, Pioneer Hi-Bred

International, Inc.How a Corn Plant Develops, Iowa State University Coop. Ext.

Related topicsModule #2: Principles of Scientific Sampling

Here s what you ll do:Beforehand♦ Decide if you’ll be doing all three activities or just the second.♦ If you’re doing activities 1 and 3, find a host farmer who’s willing to schedule two sessions for this module,

a couple of months apart.Today, on site♦ Learn how silage and grain corn respond differently to dense planting schemes;♦ Learn how soil types influence optimum harvest populations;♦ Choose and calculate a drop rate for a given soil type.



Corn Seeding Rates and

Maturity SelectionACTIVITY # 1: Preplanting Decisions on Seeding Rates

Setting TimeRequired

Materials Handouts

In a farmer s home, prior toplanting preferably, before seedhas been ordered

Group size: 2 to 10 or more

30 minutes Your state sdatabase ofsoil/yieldrelationships

Optimum Corn Seeding Rates:Grain and Silage

Q: Pose a series of questions: A:

What are the benefits of denselyplanted stands? (See resources list.)

Recent corn hybrids have been selected to perform well andproduce maximum yields when planted densely.

Anything else? Densely planted stands reduce weed pressure slightly—and leadto somewhat faster dry-down and earlier harvest for silagecorn.

Why is weed pressure reduced? Weeds controlled by herbicides or cultivation give corn an earlystart; the corn grows tall and shades the weeds.

Why faster dry-down? The lack of sun through the canopy yellows and dries the stalks.

What is a field’s yield potential?How important is it in decidinghow densely to seed your crop?

Yield potential is the sum of all the factors that affect the quantityand quality of your harvest. It has to do with soil type, fertility,drainage, the date you planted, the field’s rotationhistory—and the weather.

Too bad you never quite know till the end of the season what your yield potential was at the start. But…regardless of soil type or what the previous year’s crop was, or how cold or wet the weather was atplanting time—except in droughty soils higher planting densities provide higher yields.

Show charts or other data describing the relationship between soil type and yield potential from your state’s soildatabase.

But doesn’t soil type affect plantingdensity?

Sure it does. Deep soils with good water-holding capacity cansupport greater corn populations than can sandy or shallowsoils.


Q: Continue the discussion: A:

Why is silage corn typicallyplanted at higher rates thangrain corn?

Because it’s harvested at a different level of maturity, silage cantolerate more competition for water and nutrients. And silagequality—fiber and digestibility—remain about the same (atdensities below 35,000 plants per acre).

Hand out the worksheet Optimum Corn Seeding Rates: Grain and SilageParticipants may fill out one or both pages, naming their fields in the second column of each table and determing the

drop rate in the fourth columnaccording to whether they are using conventional or no-till planting methods. Gothrough them together, discussing each scenario as needed.

What’s the function of the “droprate”?

The drop rate accounts for the fact that some seeds won’tgerminate.

How do you calculate droprate—and why is it different forconventional and no-till fields?

To calculate, divide your target harvest population by the factor inthe table.

Seed-to-soil contact isn’t quite as good under no-till conditions.

(With no-till corn planted late—as after hay harvest—it’s better not toplan for the highest populations.)

If you plan to do Activity 3 after the corn is up, remind your host to hold on to the worksheet.You ve got just one evaluation formfor this module either hang on to them and include impressions fromboth

sessions, or photocopy an extra set for Activity 3.Remind everyone of the next class.



Corn Seeding Rates and

Maturity SelectionACTIVITY # 2: About GDDs and the 20/60/20 Rule


Materials Handouts

In a farmer s home, preferably witha table to work at. Prior toplanting best before seed hasbeen ordered.


30 minutes Pencils, clipboardsand calculators

Scrap paper

Understanding Growing DegreeDays (GDDs)

Northeast GDD Map

Planning Sheet for Corn Planting(optional)


Under what range of temperatures does corngrow best?

Below 50°F and above 86°F, corn growth just about shutsdown, especially if it’s dry. Between thosetemperatures you get steady growth, with 80°F beingabout optimum.

Hand out Understanding Growing Degree Days (GDDs) and the Northeast GDD Map.

Give this simple explanation of Growing Degree Days (GDDs) as it relates to corn growth:

The GDDs concept lumps together corn-growing temperatures (that is, temps above 50¡F but below 86¡F) for anentire growing season. This gives you a measure of how corn maturities match your climate. (Actually, there aretwo GDD methods used for corn, but this is the most common and recommended method.)

♦ Work through the example to show how degree days accumulate for corn.♦ Using the Northeast GDD Map, estimate the expected GDDs for your farm.

Use the chart (Average GDD accumulations) to explain that corn varieties are ranked as early-, mid-, or late-seasonaccording to how many total GDD hours are required to bring them to maturity.

♦ Discuss how estimated GDDs may help participants select corn varieties.Exercises 2 and 3 are optional; do them at the end of the activity.

Is a corn variety that’s rated as mid-season bya seed company or agriculturalexperiment station always going toperform as a mid-season corn for you?

Maybe not. Your microclimate may be different than onejust a few miles away. Each season is different, too.And even a few days’ variation in the growing seasoncan influence whether or not corn ripens on time.

Given so much variation from one season tothe next, and taking into account which ofyour fields are ready to plant early andwhich aren’t workable till late in thespring, what are possible plantingschemes that will hedge your bets andvirtually guarantee good yields—on time?

Go by the 20/60/20 rule: 20% full-season, 60% mid-season, 20% early-season.


Q: Continue your series of questions: A:

And the 20/60/20 rule is… Plant fields you can get into first with full-season corn. Plantthe fields you have to plant late with a short-season corn.Plant everything else with a mid-season corn.

Harvest the earlies first, then mids, then lates.

If we plant late ones first and early oneslast, won’t that be the order of harvest?

Actually, the hybrid maturity spread will override the orderyou planted them in (assuming a typical year).

You’ll maximize production by giving full-season hybrids asmuch time to mature as possible.

Designate varieties as full-, mid-, and early-season corn according to your experience and your seed salesperson sexperience.

What if we need silage very early? Consider planting some acreage of early season hybrids inyour earliest fields for late summer or early fall feedout.

Will the yields of full-season corn,planted early, be higher than yields formid-season corn—or for full-seasoncorn planted later? If so, how muchgreater?

Yes…that’s usually the case… and yields are 10 to 15 bushelshigher.

Do you need to plant at a different ratewhen you plant early?

Yes. It’s cooler early on, so the corn doesn’t germinate as well.Plant early-seeded full-season corn at rates 10 to 15%higher than what’s recommended for the soil type.

What if the soil is wet? Hold off. Planting early into compacted soil reduces yieldssubstantially.

How early is early for planting corn? Answer depends on your region:

________________________

What’s the latest you can plant a full-season corn?

Answer depends on your region:

________________________

How late can you plant mid-and early-season corn?

Answer depends on your region:

Mid-season: _______________________

Early-season: _______________________

What planting strategies would you usefor a really wet spring and earlysummer?

If it’s so late that even an early-season corn won’t fill in theears, plant late-season corn and harvest as silage. Or switchto annual forage crops such as sorghum-sudan crosses,sudangrass, or millets.

Optional: hand out the Planning Sheet for Corn Planting and have people assign fields to early-, mid-, and late-season corn using the 20-60-20 rule.

If there s time and interest, go through parts 2 and 3 of the GDD worksheet. People who find the exercise tooacademic are welcome to leave but not before you ve reminded them of the next class in the series, and set adate for coming back to check how well the planting plan worked.



Corn Seeding Rates andMaturity Selection

ACTIVITY # 3: Verifying Plant Populations


Materials Handouts

In a farmer s field after the corn hasemerged. Host farmer should have theworksheet, Optimum Corn SeedingRates: Grain and Silage from Activity 1,with answers for grain and/or silage.


30 minutes String, stakes,measuring tapes

Plant Population Card


Explain that we ll be sampling planting densities and finding out how many plants there are in several representativeplots scattered throughout the field to see how well our seeding plan actually worked. Each plot will equal 1/000of an acre.

Ask the host farmer: What was your targetpopulation?

Go through the math again as a refresher, so that everyoneremembers how we got here.

Why should we randomize our startingpoint?

It has to do with the importance of being unbiased that wediscussed earlier in this series.

How do we randomize our starting point? Avoid field margins and headlands… avoid the best or theworst in the field… when you get to an what seems tobe an average stand, look away, then push your markerinto the soil.

Why do we need to count a number of plotsscattered throughout the field, preferablyon the classic zigzag “W” pattern?

It’s another technique to reduce bias.

What else might skew our counts?Hint—what about those “turn-around”rows? It’s not always easy to control justwhere and when we turn at the field’s end.

In a wide field with a small planter, a different guess row(turn-around row) distance can affect how many plantsare in the field… and thus our ability to discover howwell our pre-season targets—intended for idealconditions—match reality.

Now it s time to actually check those calculations. Grab the stakes, the string, and the measuring tape hand out thePlant Population Cards and have at it.


Use these instructions to fill out the Plant Population Card:

1.

Measure across several rows (equaling thenumber of boxes on the planter) todetermine the average distance betweenrows. Reminder: Don’t include stats on theguess rows! Confirm with the host farmerthat the result matches the equipment setup(the spacing of planter boxes).

2.

Use the chart on the Plant Population Card to determine,for this average row spacing, how much of each rowto measure off in order to determine planting densityin 1/1000 acre. The group will measure and mark(with string and stakes) this distance in as many rowsas equal planter boxes.

3.

Assign one row to each participant. Count theplants in each row for the marked distance.

4.

Match planter box/rows to rows on the card. You mustknow which way the planter was going to avoidconfusing the outside and inside planter boxes.Record in column 1.

5.

Continue to other sites (“W” pattern); recordseveral counts. If possible, continue to matchrows with particular planter boxes. (Which,frankly, isn’t very easy to do.)

6.

When all samples are taken, compute the row averageand place it in the far right column of the data card.Add together and compute field average. Multiply by1000 to determine the planting rate for the field.

Q: A few last questions A:

Answers will vary

♦ Does the population match the farmer’s target?♦ If so, is the target a good one? [Review part 1 of this module.]♦ Are any rows (corresponding to planter boxes) consistently too high or too low?♦ Does the box need calibrating?♦ If the target is off, what changes can be made? [Possibilities: planter calibration, soil preparation, seed depth,

moisture problems, pest problems.]If there are no fields left to plant, write down the adjustments for next year.

And a reminder:

♦ Record your data!♦ Maintain your data!

♦ Share your data!♦ Know where to find it next year!


A. Optimum Corn Seeding Rates: Grain and SilageWorksheet for Activity 1

Grain:

Fill in your field name(s) as according to soil type. Select your target within the range of recommended harvestpopulations. Determine the drop rate (tilled or no-till).

Soil Conditions Field(s) Target Population atHarvest

Drop rate

Very deep loams and silt loams withhigh moisture-holding capacityandWell- to moderately well-drained loamsto clay loams

Recommended:28,000-30,000

26,000-28,000yours:______

(0.9 for tilled fields) (0.85 for no-till)

yours:_________Sandy loams, clays, or somewhat poorlydrained loams to clay loams


yours:______ yours:_________Droughty soils, including very gravelly,sandy, or shallow soils


yours:______ yours:_________

Silage

Fill in your field name(s) as according to soil type. Select your target within the range of recommended harvestpopulations. Determine the drop rate (tilled or no-till).

Soil Conditions Field(s) Target Population

at Harvest

Drop rate:

Very deep loams and silt loams withhigh moisture-holding capacity


yours:______

(0.9 for tilled fields) (0.85 for no-till)

yours:_________

Well- to moderately well-drained loamsto clay loams


yours:______ yours:_________Sandy loams, clays, or somewhat poorlydrained loams to clay loams


yours:______ yours:_________Droughty soils including very gravelly,sandy, or shallow soils


yours:______ yours:_________


B. Worksheet: Understanding Growing Degree Days (GDDs)Worksheet for Activity 2, p.1

Temperature is the major factor that determines thedevelopment and maturity of corn. Corn growsbest at temperatures above 50° but below 86°. Soif you add up—by the day or week or month or

season—all the degrees in each day that fallbetween 50 and 86, MINUS the base temperature(50°), you’ve got the accumulated GrowingDegree Days for that time period.

Here s how you do it for one 24-hour period:

Add the day’s low to the day’s high (the high being no more than 86°). Divide by two to get the averagetemperature. Subtract 50°. The result? Your accumulated GDDs for that day.

In other words:Daily maximum temperature + daily minimum temperature - 50 = x GDDs

2REMEMBER: if the day s high is over 86¡, use 86¡ for your daily max.

Exercise I:

Calculate the GDD for each of these three days: (use scrap paper)

High 78°, low 65° High 94°, low 72° High 61°, low 47°

_____ - _____ -50 = ____GDD2

_____ - _____ -50 = ____GDD2

_____ - _____ -50 = ____GDD2

♦ What are your accumulated GDDs for this three-day period? ___________ GGDs

Pretend that the daily temperatures repeated in this three-day sequence for the whole month of June.♦ What are your accumulated GDDs for the month? __________ GDDs x 10 (there are ten 3-day sequences in the 30

days of June)

To estimate the season s expected GDDs for your farm:

♦ Find your location on the Northeast GDD Map. _________

♦ Add 100 GDDs if you are on a valley floor or other area that warms up fast.

♦ Subtract 100 GDDs if you are on a high hill or in a frost pocket.Result: _________

Average GDD accumulations needed for corn development stages

Growth Stage 80 day (early) 95 day (mid) 110 day (late)

Emergence ~110 ~ 110 ~110

Silk Stage ~1,100 ~1250 ~14001/2 Milk Stage (optimal silage harvest) ~1800 ~2100 ~2400Maturity ~1900 ~2200 ~2500


B. Worksheet: Understanding Growing Degree Days (GDDs)Worksheet for Activity 2, p.2

Exercise II (optional):

To determine what s a full-, mid-, or early-season corn for your farm:

Refer to the estimated GDDs for your farm (from Exercise I).

‹ Full-season grain corn is exactly the estimated GDD.

` Silage corn is harvested at 1/2 –milk-line stage and doesn’t need as many GDDs. Subtract 100 GDDs from‹ to compensate.

´ Mid-season grain corn requires 200 -300 fewer GDDs to mature. Subtract 200, then 300, from your farm’sestimated GDDs.

ˆ Subtract 100 from ´ for mid-season silage corn.

Early-season graincorn requires even fewer GDDs to mature. Subtract 300—or more—from your farm’sestimated GDDs.

¯ Subtract 100 from for early-season silage corn.

Grain Silage Season length:

(from Exercise III, below)

Full-season:

Total expected GDD =

‹

_________ GDD

`

( -100) ________ GDD ________

Mid-season:

total expected GDD less 200,to

total expected GDD less 300) =

´

_________ to

_________ GDD

ˆ

( -100) ________ to

________ GDD ________

Early-season:

total expected GDD less 301 (or more) = _________ GDD

¯

( -100) ________ GDD ________

Exercise III

Match your GDDs to a maturity unit: Seed companies and research institutions sometimes use different methods ofcalculating GDD requirements for corn hybrids. You can convert to season-length requirements with this table:

GDDs available on your farm Season length GDDs available on your farm Season length

2350 — 2450 110 -day 1850 — 1950 85 -day

2250 — 2350 105 -day 1750 — 1850 80 -day

2150 — 2250 100 -day 1650 — 1750 75 —day

2050 — 2150 95 -day 1550 — 1650 70 -day

1950 — 2050 90 -day


C. Northeast GDD MapHandout for Activity 2


D. Planning Sheet for Corn PlantingOptional Worksheet for Activity 2

Fill in target acres for each hybrid maturity classaccording to the 20-60-20 rule and using thefollowing order:

1. List cornfields by planting time, with yourearliest field first and your latest field at the end.Note the acres of each field. (It isn’t necessary todetermine precise rankings between similarfields.)

2. Starting with the earliest field, assign fields tofull-season (F) corn. Keep track of the runningtotal (acreage). Stop assigning fields to full-season when the target is reached.

3. Starting with the next available field, assignfields to midseason (M). Start a new runningtotal. Stop assigning fields to “midseason” whenits target is reached.

4. Continue assigning fields to short season (S).

♦ Total acres in corn: ______________

♦ Target acres full season: _______________

♦ Target acres mid-season: _______________

♦ Target acres short-season: ______________

Season Running

Field ID Acres (F,M,S) Total Acres

(First Planted)

____________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ ______Field ID Acres (F,M,S) Total Acres

____________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ __________________ ___ ___ ______(Last Planted)

E. Plant Population CardWorksheet for Activity 3

Date: Growth Stage: PlantHt.

Procedure: In alfalfa use a 2 sq.ft. sampling frame to sample at least 10 areas of the field. Count number of alfalfa crowns/ 2 sq. ft.

In corn, sample 1/1000 acre units. Count number of plants/row distance for 1/1000 acre.It is recommended that you sample all rows of the planter. Make sure you record the size of your sample unit.

Sample 1 2 3 4 5 6 7 8 9 10 Average / Sq.Ft. or AcreR1

R2

R3

R4

R5

R6

SamplingUnit:

Conversions: Map:

Row Spacing (inches) 1/1000 Acre30 17ft. 5 in.

Comments: 32 16ft. 4 in.36 14ft. 6 in.38 13ft. 9 in.40 13ft. 1 in.

In alfalfa, Average ÷ Sample Sq. Ft. = Plants per Square Foot

In corn, Average Count X 1000 = Plants per Acre


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Module FeedbackCorn Seeding Rates and Maturity Selection

Tell us a little about yourself:

I m a♦ Farmer _____________♦ Crop advisor ________♦ Industry rep _________♦ Extension educator ___♦ Other _______________

My commodity area is:♦ Dairy and field crops _____________♦ Vegetables ______________________♦ Fruits and berries ________________♦ Greenhouse and nursery stock _____♦ Other ___________________________

Let us know what you think:

What part of the workshop was most interesting for you?

What part of the workshop was most valuable to you?

What two new ideas would you like to try on your farm or in your business?

Do you feel you understand IPM—and how to use it—better now?

What other information should be included in this module?

What other topics would you like us to cover in future modules?

Teachers, please fill out an evaluation as well. Photocopy and send all informative evaluations to:

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corn Seeding Rates And Maturity Selection · NE-IPM Module #12 Corn Seeding Rates and Maturity Selection p. 1 Corn Seeding Rates and Maturity Selection